Wrx gearbox help
 

My Wrx is making a very ticking noise that gets louder as i drive, i took the car to Subaru they checked the car over and diagnosed it to be the gearbox. My Transmission No: TY754VN6AA. I have looked on ebay and called breakers but no one seems to have this trans. There are no mods on the car.

The 2 questions i need help with:
- is it cheaper to replace or rebuild?
- What other Transmission will be a direct replacement- 9R-TY754VN5AA, 7R-TY754VN4AA..